Engines may include an air filer in the air intake passage for filtering air entering a turbocharger compressor (if the engine is boosted) or an intake throttle (if the engine is naturally aspirated). Air filters may become plugged over time leading to pressure drops across the filter. Accordingly, air filters may be intermittently diagnosed so that a vehicle operator can be informed about changing his filter.
Example approaches used to monitor air filter plugging involve the use of manifold air flow sensors to detect changes in air flow resulting from the plugging, the use of dedicated pressure sensors to detect pressure depression downstream if the air filter, etc. In response to filter plugging, a controller may limit engine power to reduce compressor over-speeding.
However, the inventors herein have recognized potential issues with such approaches. As one example, MAF sensor data may be less desirable than speed density data for engine control, making the MAF sensors less available. As another example, dedicated pressure sensors positioned downstream of the filter may be effective but can add substantial cost and complexity to the system.
In one approach, to at least partially address these issues, a method for an engine is provided. The method comprises, indicating filter degradation based on a pressure sensor in a crankcase vent tube. In this way, an existing pressure sensor can be advantageously used to identify air filter plugging.
In one example, an engine crankcase ventilation system may include a crankcase vent tube coupled between an air intake passage and a crankcase. A pressure sensor (or flow sensor) may be positioned within the crankcase vent tube for providing an estimate of flow or pressure of air flowing through the vent tube. During conditions when manifold air flow is lower than a threshold flow, such as during engine cranking, an engine controller may learn an offset and a reference pressure for the pressure sensor. For example, the pressure sensor may be a first pressure sensor, and based on whether the pressure sensor is an absolute pressure sensor or a gauge pressure sensor, the controller may compare the output of the first pressure sensor to a barometric pressure (BP) reading estimated by a second pressure sensor, and learn a sensor offset. Then, during conditions when manifold air flow is higher than the threshold flow, such as after engine cranking when an engine speed is sufficiently high, the controller may adjust the output of the first vent tube pressure sensor based on the learned offset, and determine air filter plugging based on a deviation of the adjusted output from the reference pressure estimated during low air flow conditions. For example, based on the adjusted output of the first vent tube pressure sensor deviation from an inferred BP estimate, air filter plugging may be determined. In response to the air filter plugging, a mitigating action may be performed. For example, a diagnostic code may be set and engine speed may be limited to reduce compressor damage from over-speeding or over-heating.
In this way, by using an existing crankcase ventilation system pressure sensor to identify air filter plugging, the need for additional sensors and valves for monitoring air filter degradation is reduced, providing cost and complexity reduction benefits without reducing the accuracy of degradation detection. By learning offsets in the pressure sensor during low engine air flow conditions and then applying the learned offsets during high engine air flow conditions, crankcase vent tube pressure may be accurately and reliably used to indicate air filter plugging. By relying on vent tube pressure, rather than MAF, to diagnose an air filter, the need for MAF sensor data in diagnosing air filter plugging is reduced. Further, the approach enables the crankcase ventilation system to remain active during a diagnostic procedure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.